The present invention generally relates to a transmission system in a ring-like local area network. More particularly, the invention is concerned with a slot access system suited advantageously for a consolidation type local area network capable of transmitting both periodically generated information and burst-type information mixedly by adopting a slot multiplex transmission.
A transmission system in which burst-type information such as messages for inter-computer communication is transmitted by dividing the information into predetermined transmission units referred to as time slots has heretofore been known, as is disclosed Kawabata et al's article entitled "Ring-Type Optical Network of 100 Mbits/Second Interlinking Bus-Type Networks" contained in Japanese literature "Nikkei Electronics" published on Dec. 5, 1983. According to this system, each of the time slots is provided at the header thereof with an indicator for indicating whether the associated time slot is in the "free (idle)" state or in the "busy (occupied)" state, wherein the transmission apparatus or station having a request to send data fetches the "free (idle)" time slot when data corresponding to one time slot has been prepared to thereby send the data by placing it in the acquired time slot. This system is certainly advantageous in that transmission suffering scarcely time lag can be realized.
As another system known in the prior art, there can be mentioned a transmission system disclosed in Japanese Patent Application No. 88455/1987 (JP-A-62-88455). According to this system, one of all the time slots is allocated with information indicating permission of transmission at the header portion, wherein the transmission apparatus or station having a request to send information or data first acquires the time slot having the transmission enabling information and then uses successively the time slots succeeding to the acquired time slot for thereby transmitting the information at one burst. With this known system, high-speed transmission can be carried out.
Both the transmission systems mentioned above have merits and demerits, respectively. Accordingly, it is desirable to adopt these transmission systems properly and selectively in dependence on the networks to which they are practically applied. To this end, however, logics of control of the transmission and management thereof will have to be made as compatible or common as possible between both systems. However, such compatibility is difficult to realize because of difference in the format for transmission between these systems, giving rise to a problem.